Basic script which allows for start/stopping with only one instance allowed to be running at a time.

stopstart

#!/usr/local/bin/python3
import os
import signal
import time
import sys

PID_FILENAME = __file__.split("/")[-1] + ".pid"


def main():
    stop = False

    def exit_handler(signum, frame):
        nonlocal stop
        stop = True

    signal.signal(signal.SIGTERM, exit_handler)
    signal.signal(signal.SIGINT, exit_handler)

    try:
        with open(PID_FILENAME, "x") as f:
            f.write(str(os.getpid()))
    except FileExistsError:
        print("main already running")
        sys.exit(1)

    while not stop:
        print("running main:", end=" ", flush=True)
        for i in range(5):
            print(i + 1, end=" ", flush=True)
            time.sleep(1)
        print()

    os.unlink(PID_FILENAME)


def stop():
    try:
        with open(PID_FILENAME) as f:
            pid = int(f.read())
    except FileNotFoundError:
        print("main not running")
        sys.exit(1)

    os.kill(pid, signal.SIGTERM)


try:
    command = sys.argv[1]
except IndexError:
    print("no command")
    sys.exit(1)


if command == "start":
    main()
elif command == "stop":
    stop()
else:
    print("invalid command")
    sys.exit(1)